I did some comparison shots of the Zeiss ZE 25f2 Distagon, ZE 35f2 Distagon and ZE 50f2 Makro-Planar lenses this morning. Boring motive and quite dizzy winter weather, but still some results.

All pictures Canon 5D2 on tripod and cable release, sharpness adjusted in life view for optimal corner sharpness. Raw file opened in ACR, CA corrected, defringe all edges, vignetting corrected, sharpness amount 60 / radius 0.5 pixel, clarity +30.

I can upload maximum four pics per message, so first here are 1400 x 700 pixel crops of the upper left corner of the 25mm lens at f2, f4 and f8. (I did pics too at f2.8, f5.6 and f11 if required)

You can make you conclusions yourself but my findings are:

+ pretty high contrast, even at f2
+ absence of blueish glow around bright areas
+ very little CA, easy to eliminate
+ already at f2 quite sharp until the last +/- 700 pixel
- the last +/- 500 pixel in corner never very sharp

Now the 35f2 lens:

+ corner sharp at f2 until last 500 pixel, at f4 until last 300 pixel, at f8 until last 100 pixel
+ CA a bit higher than the 25f2 but still low and easy to correct in ACR
- maybe slightly less contrasty than the 25f2 at open aperture
- slight blueish glow around bright areas at f2, still a bit visible at f4

There is quite a distance difference between the building in the extreme corner and the pink buildings. Perhaps it would make more sense to evaluate extreme corner sharpness by turning the camera until one of the pink buildings is in the corner.

Last not least the 50f2 MP:

+ contrasty as the 25f2
+ absence of CA
+/- very little blueish glow around bright areas at f2
+/- sharpness at f2 well until last 500 pixel, at f4 until last 300 pixel, at f8 until last 100 pixel
(for the 50 that result is +/-, for the 35 it's + coz the expectation for a 50 is higher:-)
- hmm, nothing. what u think?

Christoph

Carsten: Actually you are right, I was a bit lazy to do the test again. But actually the focus by all three lenses focussed as well as possible to the corner focus point was either infinity on the lens or "99 %" infinity. So I think using the same building (distance) would lead to quite the same result.

As soon as it is a bit warmer in Munich I would do another test outside with a tripod position orthogonal to a large building, then changing the distance to the building according the focal lengths and viewing angles of the lenses in order to achieve the same corner crops. This would make it easier to compare the results.
(But okay, the distances of focus points would be quite different.)

I think it might be helpful to see one small sized image of the entire scene taken.